Slow strain rate methods are used to quantify the degree of embrittlement in high-strength 4340 steel after coating with porous electroplated cadmium or ion-vapor-deposited aluminum and subsequently exposing to aqueous sodium chloride environments for various times. Porosity in the coatings is primarily responsible for the establishment of galvanic couples at the steel/coating interface, resulting in the generation and absorption of hydrogen in the steel. Data from hydrogen permeation and galvanic corrosion experiments are used to establish a model for hydrogen generation in coated tensile specimens. Estimates of the total hydrogen absorbed in cadmium-plated tensile specimens are consistent with the results of slow strain rate tests whereas similar calculations grossly underestimate the total hydrogen absorbed in aluminum-coated specimens where localized corrosion processes are believed to enhance the rate of hydrogen generation.